Tahamina, Islam & Ahmad, 2023

Islam, Md Niraul & Ahmad, Wasim, 2023, New nematode Tahamina indica gen. nov., sp. nov. (Nematoda, Dorylaimida, Tylencholaimoidea) from the tropical rainforest, Western Ghats, ZooKeys 1186, pp. 1-13 : 1

Tahamina gen. nov.

Tylencholaiminae Filipjev, 1934 ( Tylencholaimidae Filipjev, 1934).

Diagnosis.

Large sized nematode, 1.3-1.4 mm long body. Cuticle dorylaimoid, outer cuticle thin with very fine transverse striation, inner layer thicker than the outer, distinctly striated. Lateral chords narrow. Lip region cap-like, offset by constriction, 8.0 μm wide or one-fourth of the body diameter at pharyngeal base, labial papillae raised, lips slightly separated. Cheilostom a truncate cone. Amphidial fovea cup-shaped, aperture slit-like, occupying about one-half as wide as lip region diameter. Odontostyle short, robust, spindle-shaped, 8.0-9.0 μm long, 1.0-1.1 times lip region diameter. Odontophore simple, rod-like, 10.5-11.5 μm long with thickening or minute knobs-like structure at the base. Guiding ring simple. Pharynx consists of a slender and weakly muscular anterior part expanding abruptly into a cylindrical basal bulb, separated by constriction, occupying about two-fifths to one-half (42-50%) of the total pharyngeal length. Female genital system monodelphic-opisthodelphic with anterior uterine sac. Vulva pore-like. Tail long, elongated with a slight dorsally curved tip. Male not known.

Type and only species.

Tahamina indica gen. nov., sp. nov.

Relationships.

In the presence of a short odontostyle with a distinct lumen, odontophore with minute knobs-like structure and longer pharyngeal expansion, the new genus well fits under the subfamily Tylencholaiminae Filipjev, 1934 of the family Tylencholaimidae ( Tylencholaimoidea ).

Tahamina indica gen. nov. can be separated from Tylencholaimus de Man, 1876 in having a dorylaimoid cuticle, radial elements absent (vs. tylencholaimoid cuticle, radial elements present); vulva pore-like (vs. vulva transverse); differently shaped tail (tail long, elongated vs. tail short, rounded to conoid). The new genus differs from the Heynsnema Peňa-Santiago, Guerrero & Ciobanu, 2008 in having female genital system mono-opisthodelphic (vs. amphidelphic); vulva pore-like (vs. vulva transverse) and differently shaped tail (tail long, elongated vs. tail short, rounded to conoid).

Based on the shape and size of the odontostyle and odontophore, the expanded part of the pharynx and tail, the new genus comes close to Discomyctus Thorne, 1939 and Wasimellus Bloemers & Wanless, 1996 but differs from the former in having the inner cuticle dorylaimoid (vs. tylencholaimoid); labial disc absent and labial papillae raised (vs. labial disc present and labial papillae not raised); odontophore with thickened base or minute basal knobs-like structure (vs. odontophore with distinct large basal knobs); female genital system mono-opisthodelphic (vs. mono-prodelphic); vulva pore-like (vs. transverse) and tail elongated (vs. tail elongated to tail long filiform). It differs from Wasimellus in having a guiding ring single (vs. guiding ring double), the expanded part of the pharynx comparatively long (42-49 vs. 35-42% of total neck length), pharyngeal expansion abrupt (vs. gradual expansion); vulva pore-like without sclerotized pieces (vs. vulva transverse, with sclerotized pieces); female genital system mono-opisthodelphic (vs. amphidelphic), tail elongated (vs. tail filiform).

In the presence of a dorylaimoid cuticle, narrow lateral chord, and weakly muscular expanded part of the pharynx, the new genus resembles Dorylaimoides Thorne & Swanger, 1936, which belongs to the family Mydonomidae but differs in having a differently shaped odontostyle (odontostyle spindle-shaped, symmetrical vs. odontostyle simple, asymmetrical) and odontophore (odontophore simple rod-like with basal thickening or very minute knobs-like structure vs. odontophore angular or arcuate without basal thickening or knobs); longer pharyngeal expansion (about two-fifths to one-half vs. one-fifth to one-third of total neck length); and vulva pore-like (vs. vulva transverse).

Based on the shape of the stylet, lip region and tail pattern, the new genus is comparable to two non-tylencholaimid members Mitoaxonchium Yeates, 1973 and Hulqus Siddiqi, 1981, both belonging to the subfamily Hulqinae of the family Qudsianematidae ( Dorylaimoidea ) but it differs from the former in having a longer body size (L = 1.3-1.4 vs. 0.46-0.61 mm); shorter pharynx (b = 4.9-5.2 vs. 2.4-3.2); the position of dorsal esophageal gland nuclei more anteriorly (12-16 vs. 30% of expanded part of pharynx from its expansion), female genital system mono-opisthodelphic (vs. amphidelphic) and differently shaped vulval opening (pore-like vs. transverse). The new genus differs from Hulqus in having a longer body (L = 1.3-1.4 vs. 0.86-1.10 mm); shorter pharynx (b = 4.9-5.2 vs. 2.4-3.0); the position of dorsal esophageal gland nuclei more anteriorly (12-16 vs. 35-41% of expanded part of pharynx from its expansion), pharyngeal expansion abrupt, separated by constriction (vs. expansion gradual, without constriction) and differently shaped vulval opening (pore-like vs. transverse).